The early detection of cancer has been of foremost concern to clinicians since the advent of the disease. All manner of methods have been applied to the detection or diagnosis from non-invasive to highly invasive. Noninvasive techniques, if effective, are preferred because of the decreased risk to the patient and the decrease in the associated costs.
As with most types of cancer, breast cancer patients benefit from early detection by realizing an increased survival rate. Mammography, a noninvasive technique is currently the foremost method of screening for breast cancer. Mammography has recently been supplemented by the use of ultrasound when evaluation of lesions identified in the mammographic diagnosis is uncertain. (Mendelson, Ellen B. Ultrasound secures place in breast Ca management, Diagnostic Imaging, April 1991, pp 120-129, 157). The use of ultrasound has in the past been limited to searching for the three accepted characteristics of fluid-filled cysts (i) a smooth exterior boundary; (ii) posterior enhancement; and (iii) weak internal echoes or anechoic. (Jackson, V. P., The Role of US in Breast Imaging, Radiology, 177: pp 305-311, 1990). If any of these characteristics is missing or cannot be clearly detected by the ultrasound, because the lesion contains cellular debris or is too small, it is common to perform a biopsy to conclusively determine whether the lesion is a solid mass which is possibly malignant or whether the lesion is merely a fluid-filled cyst.
However, despite the desire to use ultrasound, because of its safety, easy of use and low cost, current techniques are not very reliable in conclusively identifying the above-referenced characteristics of fluid-filled cysts. As a result, it is often still necessary to perform a biopsy to distinguish between a solid mass and a fluid-filled cyst.
The recent development of color flow Doppler has lead to a great deal of research being performed in the area of velocity detection in various organs or systems in the human body (Eyer et al. Color Digital Echo/Doppler Image Presentation, Ultrasound in Med. & Biol., Vol. 7, pp 21-33). For example, two popular areas of velocity detection research include the circulatory system (U.S. Pat. No. 5,109,857 assigned to Applicant) and blood pool analysis in the heart (U.S. Pat. No. 5,211,169 to Freeland). Such techniques use a color video to represent the image which is generated by the ultrasound transducer. The movement of a fluid, for example blood, toward the transducer can be represented by red, an arbitrarily selected color. The movement of fluid away from the transducer has commonly been represented by blue, another arbitrarily selected color. Stationary objects are represented by shades of grey, with lighter shades of gray indicating more strongly reflecting objects.
A focus of current ultrasound research is the use of color flow Doppler, in the context of breast cancer diagnosis, to determine if a blood flow exists once a lesion has been determined, by means of the above-referenced diagnostic techniques. The existence of specific types of blood flow in a solid lesion is considered by some to be indicative of a cancerous tumor.
Ultrasound is a sound pressure wave which has in the past been used exclusively to sense the structure of tissue or to sense motion. Simply stated, ultrasound has been a means of passively measuring or sensing both the structure of tissue and the presence or absence of fluid motion. To date, applicant is unaware of any research or testing which has been performed to use an ultrasound device to actively induce movement of fluid within a lesion within the human body. The purpose for doing so would be to distinguish between a fluid-filled cyst and a solid mass to supplement mammography or to conduct an initial screening for lesions independent of mammography. The use of ultrasound would be a very valuable, safe, noninvasive and cost effective method of determining the nature of any lesions located during screening for breast cancer. In addition, such a technique would greatly reduce the number of unnecessary biopsies which are required because of the inability of current ultrasound techniques to conclusively determine if a lesion is solid or fluid-filled.
In addition to the above-mentioned medical uses, ultrasound is currently being used in a wide range of industrial applications. These include, for example, the inspection of steel plates, aircraft wings, turbine blades, ball bearings, and in flow measurements of gas and coal pipelines. Ultrasound is also used to monitor the curing of cheese and the status of cell cultures in bioreactors. In both of the latter applications, a device which can noninvasively distinguish between the solid and liquid states of a material would be beneficial. For example in cheese-making, the ability to determine the liquidity or solidity of a cheese wheel's core without cutting into it would save money and time. In a bioreactor, the ability to remotely monitor the clumping or gelling of cellular material would also be advantageous.